The invention relates to a two-wheel folding bicycle, which can be folded together in the plane of the bicycle frame, having a main frame, on whose rearward frame section a seat pillar can be fastened and on whose forward frame section a front wheel fork is rotatably disposed, and having a rearward rigid frame for receiving the rear wheel axle.
German Patent Document DE 43 11 998 A1 shows such a folding bicycle having a main frame which is-divided into several mutually hinged frame tubes. These frame tubes are adjoined toward the rear by a rigid partial frame for receiving the rear wheel axle. An upper tubing of the main frame is divided into two tube sections which are also hinged to one another and can be fixed by means of the hinge point on a lower tubing. If the connection is opened up at this point, the main frame can be pushed together like a shears-type frame with rigid and movable joints in the direction of the rearward partial frame.
A similar construction is illustrated in U.S. Pat. No. 5,069,468, with the difference that here a steadying strut connects the upper tubing with the lower tubing and is displaceably held on the lower tubing. In the ready-to-ride condition, however, the steadying strut is fixed on the lower tubing. In the case of this known embodiment, all frame components are always connected with one another during the folding.
It is an object of the invention to provide, in the case of the folding bicycle of the above-mentioned type, a main frame which is stable and resistant to deformations when the bicycle is used and which permits the folding-together of the bicycle by means of a few manipulations.
According to the invention, this object is achieved by providing a folding bicycle of the above-noted type wherein the main frame is also designed as a rigid frame, wherein the main frame and the partial frame can be folded together by way of at least two hinged supports in the frame plane, wherein each hinged support is hinged by means of its one end by way of a first hinge on the main frame and, by means of its other end, by way of another hinge on the partial frame, and the axes of rotation of all hinges extend in parallel to one another and perpendicularly to the frame plane, and wherein a re-leasable connection fixes the partial frame on the main frame of the characteristics of the main claim. Advantageous further developments of the invention are contained in the subclaims.
According to the invention, in addition to the partial frame, the main frame also has a rigid design and thus provides the bicycle frame as a whole with sufficient stiffness. Viewed in the direction of the plane of the bicycle frame, the two hinged supports form a four-point hinge chain by means of their hinge points. As the result of this hinging, the rearward partial frame, together with the rear wheel, after the release of the fixing, can be swivelled without effort toward the front in the direction of the main frame and can be placed tightly against the main frame, so that the folding bicycle as a whole can be folded together to a small size. However, it should be pointed out that the invention is not necessarily limited to two hinged supports. Thus, according to the requirements, each hinged support or only one hinged support may be designed as a double hinged support which is divided into one support respectively on both sides of the frame plane.
In the collapsed position, the main frame and the partial frame may optionally be fixed by a splint or similar device in order to be able to better handle the folding bicycle when storing it, for example, in a trunk of a motor vehicle.
In the simplest case, the rear partial frame is rigidly connected with the main frame. However, the construction of the folding bicycle according to the invention also permits the arranging of the rearward partial frame in a resilient manner with respect to the main frame. For this purpose, a damper-spring unit, which is known per se, is provided in the area of the fixing of the two frame parts. However, in certain riding situations, for example, when riding uphill, it may be desirable to stop the resilience, for example, by means of a simple splint between the partial frame and the main frame.
In order to eliminate propulsion influences, it is also advantageous to dispose the pedal crank for the chain drive of the rear wheel on the partial frame. Furthermore, it is advantageous for the stability of the bicycle during the ride for the instantaneous center of rotation resulting from the hinged supports, about which the rearward partial frame swings during compression movements, to be situated in the area of the axis of the bottom bracket ball bearing. In this case, the instantaneous center of rotation is defined by the intersection point of the lengthened connection lines between the axes of rotation of the two hinges of the respective hinged support. Its position moves corresponding to the compression movements of the rear wheel. Where it is precisely situated in the starting situation, thus, when the load is normal, depends on the respective wishes with respect to the riding characteristics and correspondingly on the set angles of the hinged supports.
For reasons of production and cost, it is also expedient to provide both hinged supports with an identical shaping.
If, in the case of the bicycle according to the invention, a longitudinal control bar rotationally disposed on the main frame guides the front-wheel fork, it may be advantageous--for reducing the constructional expenditures--, to combine the upper hinge of the forward hinged support with this hinge of the longitudinal control bar. In this case, the axes of rotation of both hinges will coincide.
Additional advantageous further developments of the invention are indicated in the following description of an embodiment by means of the pertaining drawing.